This invention relates to improvements in a diaphragm pump of the type which discharges a pump fluid continuously by a diaphragm defining a pump chamber and a drive chamber.
A diaphragm pump according to the prior art has a structure shown in FIGS. 1 through 4. As illustrated in FIG. 4, a diaphragm 4 defining a pump chamber 2 and a drive chamber 3 is provided on one end of a reciprocating rod 1, and a diaphragm 7 defining a pump chamber 5 and a drive chamber 6 is provided on the 1. The diaphragm pump has a controller 8 and changeover control valves 9 and 10. When the reciprocating rod 1 is driven to one (a first) side (in the direction of arrow A), as illustrated in FIG. 1, a driving fluid (air, for example) is supplied to the drive chamber 3 on the first side of the reciprocating rod 1 to expel the pump fluid from the pump chamber 2 on this side. Meanwhile, driving fluid (air) in the drive chamber 6 on the other (a second) side of the reciprocating rod 1 is exhausted, during which time pump fluid is drawn into the pump chamber 5 on this side. FIG. 2 shows the conditions which prevail during the driving of the reciprocating rod to the first side.
When the control rod 1 reaches its stopping position on the first side, this stopping position is sensed by a proximity sensor 11, as depicted in FIG. 3, in response to which the changeover control valves 9, 10 are changed over so that driving fluid is supplied to the drive chamber 6 on the second side of the reciprocating rod 1 to drive the reciprocating rod 1 to this side (the direction of arrow B) and expel the pump fluid from the pump chamber 5 on this side. Meanwhile, driving fluid in the drive chamber 3 on the first side of the reciprocating rod 1 is exhausted, during which time pump fluid is drawn into the pump chamber 2 on this side. When the reciprocating rod 1 reaches its stopping position on the second side, this stopping position is sensed by a proximity sensor 12, as depicted in FIG. 4, in response to which the changeover control valves 9, 10 are changed over again to repeat the foregoing operation. Thus, the reciprocating rod 1 is reciprocated repeatedly to discharge the pump fluid continuously by this reciprocating motion.
During the reciprocation of the reciprocating rod 1, there are occasions where the pressure of the pump fluid expelled from one of the pump chambers exceeds the pressure of the driving fluid in the neighboring drive chamber for some reason. For example, if the pressure of the pump chamber surpasses the pressure in the drive chamber 3 for some reason during the movement of the reciprocating rod 1 to the first side (i.e., during the discharge of the pump fluid), there is the danger that the diaphragm 4, which should expand toward the side of the pump chamber 2, will contract toward the drive chamber 3, as indicated by the dashed line 4' in FIG. 2. This is referred to as a diaphragm reversal phenomenon. This phenomenon occurs also in a case where the pressure in the pump chamber 2 surpasses the pressure in the drive chamber 3 during movement of the reciprocating rod 1 to the second side (i.e., during the intake of the pump fluid into the pump chamber 2). (See the dashed line 4' in FIG. 3.)
When the diaphragm reversal phenomenon occurs, a situation arises in which stable, quantitatively accurate discharge of the pump fluid cannot be performed. If the diaphragm reversal phenomenon occurs frequently, moreover, the pump fluid undergoes agitation within the pump chamber. If the pump fluid contains fibers, the fibers will be destroyed by agitation resulting from the reversal phenomenon. If the pump fluid contains air bubbles, the air bubbles will be destroyed by agitation. Such destruction of fibers or air bubbles is undesirable. Furthermore, the service life of the diaphragms is shortened by the reversal phenomenon. This makes necessary the frequent replacement of the diaphragms and results in prolonged downtime. If the diaphragms tear because of shortened service life, outflow of the pump fluid can occur. This can result in a dangerous situation if the pump fluid is a toxic or hazardous substance.